1. Field of the Invention
The present invention relates to a line printer for simultaneously printing characters etc, while feeding print paper in units of lines.
2. Description of the Related Art
Heretofore, a line printer for simultaneously printing characters etc. according to a print signal input from a host, feeding print paper in units of line has been used.
FIG. 4 is a side view showing the outline of a print paper feeding mechanism in a general line printer.
As shown in FIG. 4, when a stepping motor 401 is rotated counterclockwise by a predetermined amount as shown by an arrow, the above-mentioned rotation is transmitted to a platen roller 404 via two gears 402 and 403. As a result, the platen roller 404 is rotated clockwise and feeds print paper 405 in units of lines. In a synchronous matter therewith, the printer prints characters etc. in response to a print signal from a host (not shown) by driving a print head 406, while feeding the print paper 405 in units of lines.
FIG. 5 is a timing chart showing a conventional driver signal in the case that the stepping motor 401 is driven. When printing according to a print signal is executed in an area A and is completed, a driver signal to the stepping motor 40i is stopped in an area D and the stepping motor 401 is stopped. In the next operation, first, a driver signal of the same phase as a supplied phase when the stepping motor 401 is stopped, is supplied, to align the position (area E). Thereafter, the printing operation is started (area G) by supplying a driver signal of the next phase.
When a driver signal sent to the stepping motor 401 is stopped and the stepping motor is in a state in which it is not excited, a counterclockwise force is applied to the shaft of the platen roller 404 by the spring force of the platen roller 404, because the print head 406 is fixed. As a result, a clockwise torque is applied to the stepping motor 401 via the gears 403 and 402. When the above-mentioned torque exceeds inhibiting torque that the stepping motor 401 per se has, the stepping motor 401 is rotated clockwise.
Therefore, when the stepping motor 401 is next driven, a phase output from a motor control circuit and the actual phase of the stepping motor 401 are asynchronous. Therefore, when a driver signal of the same phase as a phase when the stepping motor 401 is stopped, is supplied to the stepping motor 401 (area E of FIG. 5) so as to drive the motor next, if the stepping motor 401 is reversed by more than two steps, the motor is reversed to the same phase before four steps or steps of a multiple of four from a position where the stepping motor 401 is stopped, and printing is started from the above-mentioned position (area G of FIG. 5). Accordingly, there arises a problem in that printing for the four steps or the steps of the multiple of four is packed at the head.
To prevent the above-mentioned situation, a method of supplying holding current of low voltage to the stepping motor 401 while the stepping motor 401 is stopped is also conceivable. However, consumed current is increased and it is particularly a large problem in a line printer driven by a cell.